Citrix have published a guide (http://support.citrix.com/article/CTX123736) on creating a customised logon page for each virtual server, based on the FQDN received. The article works, and true to its intended aim, the sites respond on the relative FQDN and return the correctly customised login page for each of the vServers.
Once this has been completed though, the vServer that has been configured with a Responder in the NetScaler will no longer be able to use email based discovery or automatic configuration using the external store name. The error we were getting on the receiver was this:
“Your account cannot be added using this server address. Make sure you entered it correctly. You may need to enter your email address instead.”
The same error was displayed if using the email address or the FQDN of the vServer.
Disabling the Responder rule that was created following the KB allowed the configuration to work. Based on this, I fully removed the responder and in started looking for other ways to accomplish the customisation.
These are the steps that I took to enable the rewrite rule:
I am running NetScaler 10.5
Using the GUI:
1. Check that rewrite is enabled in System –> Settings –> Configure Basic Features.
2. Go to AppExpert –> Rewrite –> Actions. Create a new Action. Enter a name and set the type to Replace. In the ‘Expression to choose target location’ field, enter ‘HTTP.REQ.URL’. In the expression to replace with, you need to enter the full web address to the newly created custom logon page. In this example I have entered “https://myseconddomain.co.uk/vpn/index_custom.html”. It should look similar to the image below. Click Create when you are done. 
3. Go to AppExpert –> Rewrite –> Policy. Create a new Policy. Enter a name and set the Action to the name of the action created in step 2. The Undefined-Result-Action should be set to ‘Global-undefined-result-action’. In the expression enter the following, substituting in your FQDN: ‘HTTP.REQ.HOSTNAME.CONTAINS(“myseconddomain.co.uk”) && HTTP.REQ.URL.CONTAINS(“index.html”)’
4. Finally, we need to bind this policy to the Global HTTP Request receiver. Go to AppExpert –> Rewrite –> Policy. Select the policy that you just created, and then click Policy Manager at the top. Accept the default settings for the Bind Point (show below for completeness). Click Continue. Select Add Binding, then choose the Policy that you created in step 3. The other details can be left as default, and click Bind, then click Done in the Policy Manager.
5. Test, and hopefully all will work.
Using the CLI:
1. enable feature rewrite
2. add rewrite action REWRITE_ACT replace “HTTP.REQ.URL” “\”https://myseconddomain.co.uk/vpn/index_custom.html\””
3. add rewrite policy REWRITE_POL “HTTP.REQ.HOSTNAME.CONTAINS(\”myseconddomain.co.uk\”) && HTTP.REQ.URL.CONTAINS(\”index.html\”)” REWRITE_ACT
4. bind rewrite global REWRITE_POL 1 END -type REQ_DEFAULT
5. Test
Following this, both the custom page redirection, and email based discovery both working as they should.
